1. Field of the Invention
The present invention relates generally to a seat lifting device, and more particularly to a seat self-lifting device for a portable chair.
2. The Prior Arts
A conventional collapsible and portable chair usually uses two pivotal structures to pivotally connect the seat to an inner side of the front leg, such that the seat can flip upward. In particular, the seat can be managed from a horizontal deployed position to a vertical collapsed position by manually flipping the seat. Because such operation is cumbersome, certain portable chairs include a seat collapsing mechanism. The conventional seat collapsing mechanism usually includes a tension spring whose one end is connected with a bottom of a seat frame and another end of the spring is connected with the front leg. When the seat is in a horizontal deployed position, the spring is extended. When the pressing force to deploy the seat is released, the extended spring is released to flip the seat to the vertical collapsed position. However, using the tension spring has the following drawbacks. (1) Some of the portable chairs are provided with abutting elements to prevent the seat from over-flipping. The spring may flip the seat too fast, which causes the seat to impact against the abutting elements of the portable chair and therefore makes noise. (2) The seat collapsing mechanism is entirely exposed under the seat, which is likely to injure the user. (3) The tension spring is more likely to subject to elastic fatigue or being over-stretched, which results in malfunction of collapsing operation.